Semiconductor devices with electrical contacts are used in different technical areas, for example in memory products. In the field of dynamic random access memories as well as logic an flash chips, the electrical contacts between semiconductor material and conducting metal layers are of interest. However, also in other technical fields, electrical contacts between conducting lines and semiconductor material are of interest and the invention may be applied. By producing the electrical contact between metal and the semiconductor material it is necessary to provide a good electrical contact, i.e. low Ohm resistance between the metal and the semiconductor material. On the other hand, it is necessary to reduce the junction leakage that may be caused by the semiconductor and metallic contact.
It is known in the art to provide a silicon substrate and to produce areas with silicide on the substrate. Silicide is an alloy of silicon and metal and is formed by the reaction of a refractory metal or an almost noble metal with silicon. Silicides are used in a variety of applications. For example, silicide may be used at the source/drain and/or gate area of a transistor, or it may be used to construct a gate or local inter-connecting lines, for example. A silicide is typically formed by depositing a metal layer on a silicon layer, and then annealing the semiconductor/metal structure. When the metal is in contact with the silicon, a silicide is formed. Silicide materials are commonly used in advanced CMOS technology. Silicides reduce sheet resistance and contact resistance, which is particularly advantageous when a silicide is disposed over the source, drain and gate region of a transistor, as an example. Titanium silicide (TiSi2) has been used widely in CMOS technologies in the past, although cobalt silicide (CoSi2) rather than titanium silicide is used as a silicide material, particularly in smaller scale CMOS technologies, such as sub-quarter-micron feature sizes. However, for obtaining a good resistive contact with a minimized leakage current it is necessary to control accurately the annealing temperature and the annealing time.
For high aspect ratios of contact holes, it is known to prefill the contact holes with polysilicon to reduce the high aspect ratio and then to fill up the contact hole with metal, i.e. tungsten (W).
Additionally, U.S. Pat. No. 5,858,183 discloses producing an electrical contact on a semiconductor material by depositing firstly a titanium layer, then by depositing a titanium nitride layer on the titanium layer and additionally by depositing a tungsten layer on the titanium nitride layer. The titanium layer provides a good adhesion and a low contact resistance between the metallization and the semiconductor material. When a tungsten layer is used as a conductive top layer deposited by means of a usual chemical vapour deposition process, the titanium nitride layer serves as a barrier to prevent chemical reactions between the titanium and the fluorine which is formed during such a chemical vapour deposition process. The titanium nitride may be deposited by physical vapour deposition (PVD), chemical vapour deposition (CVD) or metal organic chemical vapour deposition (MOCVD).